Molecular Characterization of Bacillus thuringiensis Strains from Native Soils in Southern Zone of Andhra Pradesh, India

In search of novel insecticidal Bacillus thuringiensis strains effective against Spodoptera litura, a total of 44 cultures were isolated from 205 soil samples collected in Nellore district, Andhra Pradesh, India and evaluated against third instar Spodoptera litura. The isolates exhibiting more than 50 per cent larval mortality were chosen for molecular characterization with 14 cry gene primers specific to Lepidoptera. The bioassay studies indicated that, larval mortality of 86.67 per cent was observed with N30 at 168h after treatment, followed by N3 with 83.33 per cent which were comparable with standard check HD-1 (96.67%). The Other promising isolates, N44, N48 (%), N58 %), N93 %), N115 (%) and N141 which were statistically on par with each other. Molecular characterization of virulent B.thuringiensis strains with cry gene specific primers indicated that cry1I gene was predominant in present B. thuringiensis collection and it was reported from seven (N20, N23, N30, N63, N93, N141, N143) strains. The most effective strain, N30 harboured a combination of three cry genes i.e., cry1, cry2 and cry9. N3 contained only one cry gene (cry1C). Among the 19 strains characterized, N93 possessed the highest diversity with five cry genes (cry1Aa, cry1C, cry1I, cry2A(a)1, cry9Ca1). The study identified potential B. thuringiensis strains with diverse cry gene profiles encoding insecticidal crystal proteins. The presence of multiple cry genes (cry1, cry2 and cry9) in N30 likely contributed to its superior efficacy against test insect, S. litura. This strain shows promise for development into a cost effective B. thuringiensis formulation for use as a biopesticide and may also serve as a valuable resource for developing Bt transgenic crop plants.